Add a comprehensive Contributing guide (CONTRIBUTING.md) with:
- Mandatory communication requirements before starting work
- Detailed issue reporting guidelines with templates
- Complete development setup and workflow instructions
- Code quality standards and testing requirements
- Pull Request process with Conventional Commits guidelines

Polish existing documentation:
- Improve CONTRIBUTING.md formatting and clarity
- Reorganize README.md Development section with quick command reference
- Add contributing page in website docs pointing to the guide

The guide emphasizes the importance of communication with maintainers
before starting work to maximize the chances of contribution acceptance
and prevent wasted effort.